Water-use strategies and functional traits explain divergent linkages in physiological responses to simulated precipitation change.

As a part of global climate change, precipitation patterns in arid regions will change significantly, and the different responses of desert plants to these changes will lead to alterations in community composition, thereby impacting ecosystem stability. Thus, understanding the mechanism underlying the associations among physiological response variables considering changing precipitation is crucial. Here, water-use strategies, functional traits, and physiological processes (e.g., photosynthesis (A), transpiration (T), leaf water potential (Ψ), stomatal conductance (g), and soil respiration (R)) were measured in a precipitation experiment with two coexisting desert riparian species to determine how water-use strategies and functional traits operate together in generating physiological response mechanisms. The results showed that the two species exhibited divergent response pathways of physiological processes following rainfall events, although both were identified as isohydric plants with stringent stomatal regulation. For the shallow-rooted species N. sphaerocarpa, g was sensitive to changes in both surface soil moisture (S) and Ψ, and S was the primary factor influencing R. These results were supported by the preference for shallow water and predominance of functional traits associated with drought avoidance. For the deep-rooted species R. soongorica, variations in g were decoupled from S and directly influenced by enhanced Ψ, A was the main factor affecting R, while Ψ negatively affected R. These correlations could be attributed to the preference for deep water and functional traits associated with drought tolerance. These findings suggest that R. soongorica had a stronger tolerance to environmental water deficits and may expand extensively under drier climatic conditions in the future.